BIS - Bispectral Index Monitoring

Question 1

What are the 3 components of anesthesia?

Answer 1

1. Analgesia
2. Unconsciousness/hypnosis
3. Muscle relaxation

Question 2

What are the levels of (Un)Consciousness?

Answer 2

• Perception and explicit memory
• Perception and no explicit memory
• No perception and implicit memory
• No perception and no memory

Question 3

Explicit Memory:

Answer 3

Intentional or conscious recollection of prior experiences

Question 4

Implicit Memory:

Answer 4

Information not associated with any conscious recollection; Recall may occur during dreaming, hypnosis, or other psychological methods

Question 5

What is the one of the worst things a patient can suffer?

Answer 5

Awareness under anesthesia

Question 6

Deeply anesthetized patients can be influenced by which stimuli w/o being able to recall them?

Answer 6

Auditory

Question 7

Implications of recall:

Answer 7

-Pyschological sequelae
 \+Anxiety
 \+Sleep disorders
 \+Depression
 \+Nightmares
 \+Panic attacks
 \+Emotional numbing
 \+Sense of unease
 \+Anger
 \+Long-term psych disorders
 \+Hyperarousal

Question 8

Clinical signs to measure depth of anesthesia

Answer 8

• HR
• BP
• Sweating
• Lacrimation
• Pupil diameter

Question 9

Isolated Forearm Technique

Answer 9

Tourniquet is applied to one arm prior to administration of muscle relaxant
-Spontaneous mvmt or mvmt to command indicates light anesthesia

Question 10

Skin impedence

Answer 10

A quantitative measure of sweat production (Factor such as atropine and autonomic neuropathy that affect sweating reduce accuracy)

Question 11

Surface Electromyelogram (EMG)

Answer 11

Used to measure depth of anesthesia

Question 12

Which device has been most widely applied technology for measuring anesthetic depth?

Answer 12

Electroencephalography (EEG) (Although raw EEG difficult to accurately and consistently interpret)

Question 13

What is a good choice for measuring patient consciousness and why?

Answer 13

Auditory evoked potential w/EEG or alone b/c it is the last sense to be suppressed by anesthesia.

Question 14

Similar monitors to the BIS:

Answer 14

• Narcotrend
• Entropy
• Cerebral State Index
• Snap Index

Question 15

In the BIS Monitor, a forehead sensor gathers ___ and ___ data.

Answer 15

EEG, EMG

Question 16

BIS Index Ranges:

Answer 16

0: Flatline EEG
1-20: Burst suppression
20-40: Deep hypnotic state
40-60: General Anesthesia (Low probability of explicit recall, unresponsive to verbal stimulus)
60-80: Moderate Sedation (Responds to loud commands or mild prodding/shaking)
80-100: Awake (Responds to normal voice)

Question 17

BIS Marketing

Answer 17

Focused on use to prevent awareness under anesthesia; also to prevent anesthetic overdose

Question 18

How does BIS work?

Answer 18

Analyzes analog EEG signal in several ways and incorporates facial EMG. Data is analyzed and multiple data points are plugged into propriety algorithm to produce BIS value from 0-100.

Question 19

BIS algorithm was developed:

Answer 19

by studying hypnotic endpoints (eg. loss of response to verbal command) along with subsequent memory testing

Question 20

Electroencephalography (EEG):

Answer 20

A recording of electrical activity along the scalp; arises from ion currents across the cell membrane of neurons with similar spatial orientation
(Pyramidal neurons of cortex contribute most to EEG signal)

Question 21

EEG Waves: Beta (β)

Answer 21

15-30 Hz: Awake, Conscious

Question 22

EEG Waves: Alpha (α)

Answer 22

8-13 Hz: Eyes closed, meditation, Drug effects (propofol, inhaled agents)

Question 23

EEG Waves: Theta (

Answer 23

4-8 Hz: Light Sleep (Stage 1 & 2)

Question 24

EEG Waves: Delta (Δ)

Answer 24

0.5-4 Hz: Deep sleep (Stage 3 & 4)

Question 25

EEG Analysis: First Order Analysis

Answer 25

Looks at the amplitude, mean and variance; identifies periods of EEG suppression

Question 26

Suppression (in EEG)

Answer 26

at least a 0.5 second interval during which the EEG voltage does not exceed ± 5.0 mV

Question 27

SR = Suppression Ration

Answer 27

The percentage of time over the previous 63 seconds that the EEG waveform exhibited suppression

Question 28

EEG Analysis: Second Order Analysis (Power Spectrum)

Answer 28

Fourier analysis of the EEG waveform parses out the individual frequency components, creating a power spectrum; displayed as a compressed spectral array (CSA) or density spectral array (DSA)

Question 29

SEF: Spectral Edge Frequency

Answer 29

The frequency below which a certain percentage of the power of a signal is located; SEF95 is commonly used; studied as an independent predictor of anesthetic depth (cutoff in the range of 14-15Hz)

Question 30

EEG Analysis: Third Order Analysis (Bispectral)

Answer 30

Measures the correlation of the phase between different frequency components; may be helpful for noise reduction

Question 31

BIS Algorithm:

Answer 31

-Incorporates SR, power spectrum analysis, bis analysis of frontal EEG as we as facial muscle EMG (EMG is relatively highly weighted component)
-BIS values between 0 and 20 are based on a single variable -> the SR (linear relationship)
+SR 50 = BIS 20
+SR 100 = BIS 0

Question 32

SQI (Signal Quality Index) may sometimes miss what sources of noise?

Answer 32

• Electrocautery
• Forced air warmer
• Cardiac Pacemaker
• Hair shaver

Question 33

Limitations of BIS:

Answer 33

• Signal processing lag time (12 - 155 sec)
• Failure to account for certain drugs with known anesthetic effects (Ketamine, N2O, Xenon, Dexmedetomidine, SEVO and ISO)
• Paradoxical changes (Increase in BIS with deepening anesthetic; Decrease in BIS just prior to awakening)
• Pathophysiological conditions leading to reduction in BIS (Hypoglycemia, decr. in CBF, focal or global brain pathology, hypothermia)
• β-adrenergic agents (epi, ephedrine, isoprterenol) shown to increase BIS